1. Field of the Invention
The present invention pertains to novel antifoaming agents comprising 1-secondary or 1-tertiary alkyl- or 1-cycloalkyl-hexahydro-2-pyrimidinones and 1-secondary or 1-tertiary alkyl or 1-cycloalkyl-2-imidazolidinones.
2. Description of the Prior Art
Acid gas scrubbing processes are of considerable industrial importance. Most acid gas scrubbing processes involve contacting a gas stream with an aqueous alkaline solution and absorbing the acid gas, principally carbon dioxide and hydrogen sulfide, into the solution and regenerating the solution in a separate stage. The regenerated solution is then recycled to the absorption stage. One of the problems encountered in acid gas scrubbing processes is excess foaming, i.e., aqueous alkaline solutions have a natural inclination to foam, and the passing of a gas into a foamable solution is classic to the production of a foam. Consequently, resort to the use of antifoaming agents as additives to the aqueous acid gas scrubbing solutions is a common practice in the art.
There are many commercially available antifoaming agents. These antifoaming agents find a plurality of uses. However, the selection of an antifoaming agent in acid gas scrubbing processes is dependent upon several variables unique to acid gas scrubbing processes. The antifoaming agents of the present invention are particularly suited for acid gas scrubbing processes.
The following U.S. patents were considered in connection with the present invention:
______________________________________ U.S. Pat. Nos. ______________________________________ 2,176,441 3,848,057 2,608,462 3,862,243 2,674,619 3,943,227 2,712,978 4,002,721 2,946,652 4,042,528 3,071,433 4,094,957 3,275,403 4,100,257 3,642,430 4,101,633 ______________________________________
None of these patents disclose, teach or suggest 1-substituted cyclic ureas (i.e., 1-substituted hexahydro-2-pyrimidinones and 1-substituted-2-imidazolidinones) and/or their use as antifoaming agents in acid gas scrubbing processes. Many of these patents teach acid gas scrubbing processes and the use of antifoaming agents in their respective processes. Of particular interest are U.S. Pat. Nos. 4,094,957; 4,100,257; and 4,101,633, in addition to U.S. Pat. Nos. 4,112,050; 4,112,051; and 4,112,052, the disclosures of which are incorporated herein by reference. These patents and patent applications teach and disclose the use of sterically hindered amines, alone, or in combination with other acid gas scrubbing compositions in acid gas scrubbing processes. These patents and patent applications point out that there are three principal types of acid gas processes, i.e., the aqueous amine process (amine and water constitute the acid gas scrubbing solution), the "hot potash" process (an inorganic alkaline material such as potassium carbonate activated by at least one amine) and the organic solvent process (an organic solvent such as sulfolane used in combination with an amine). Foaming problems are especially troublesome in the "hot potash" type processes such as described and claimed in U.S. Pat. No. 4,094,957 and U.S. Pat. No. 4,112,050.
The prior art has included disclosures of some cyclic ureas for applications in the textile and pharmaceutical industries. For example, German Pat. No. 1,121,617 discloses the reaction of urea with 1,3-propanediamines of the formula R'--NH--CR.sub.2 --CR.sub.2 --CR.sub.2 NHR, wherein R' is alkyl-, cycloalkyl-, hydroxyalkyl-, aryl- or aralkyl radicals and R is the same as R' or a hydrogen atom. This German patent does not specifically disclose the instantly claimed antifoaming agents or their use as antifoaming agents in acid gas scrubbing processes. Swiss Pat. No. 357,400 discloses the reaction of urea with N-substituted 1,3-propanediamines of the formula: R--NH--CH.sub.2 --CH.sub.2 CH.sub.2 --NH.sub.2, wherein R is hydrogen or an aliphatic radical having 1-18 carbon atoms.